High frequency apparatus



April 16, 1957 CHAO c. WANG HIGH FREQUENCY APPARATUS 4 Sheets-Sheet 1 Filed Nov. 25, 1950 v b WH WK? N WN 2 luv- INVENTOR 67/40 Cf W4/V6 Q dZM ATTORNEY April 16, 1957 CHAO c. WANG HIGH FREQUENCY APPARATUS 4 Sheets-Sheet 2 Filed Nov. 25, 1950 INVENTOR C7640 C WQ/VG AT I'ORNEY April 16, 1957 CHAO c. WANG HIGH FREQUENCY APPARATUS 4 Sheets-Shee't 3 Filed Nov. 25, 1950 INVENTOR C3740 C. Wfl/VG ATTORNEY April 16, 1957 CHAO c. WANG HIGH FREQUENCY APPARATUS 4 Sheets-Sheet 4 Filed Nov. 25, 1950 INVENTOR C9440 Cf W4A/6 fi m? 714m A'l 'TORNEY NNK United States Patent HiGH FREQUENCY APPARATUS Chao C. Wang, Bayside, N. Y., assignor to Sperry Rand Corporation, a corporation of Delaware Application November 25, 1950, Serial No. 197,535

12 Claims. (Cl. 315-35) This invention relates to slow wave propagating electron discharge devices and, more particularly, to means for pulsing such devices.

Electron discharge devices including slow electromagnetic wave energy propagating structures or travelling wave tubes are becoming increasingly important in microwave transmission systems. Travelling wave tubes have satisfactory efiiciencies and gain properties compared to other microwave tubes and, in addition, are characterized by noise figures which are superior to other microwave devices. More important, however, at the present time is the extremely superior bandwidth characteristics of travelling wave devices as compared to other microwave tubes.

In many microwave transmission systems it is desirable to employ electromagnetic energy of an intermittent or pulsed variety. According to one form of the present invention, means are provided for pulsing slow wave propagating devices. According to another form of the present invention in connection with a slow wave propagating structure means are provided for pulsing an electron beam focusing means in synchronism with an electron beam producing means.

In another aspect the present invention provides for the elimination of any external electron beam focusing means, such as a solenoid coupled to the electron beam. This may take the form of introducing direct current into the ends of the slow wave propagating structure, such as a helix, whereby such current is efiective for maintaining a suitable magnetic focusing field. In this arrangement, the magnetic focusing field may be established only substantially during the time that electrons are traversing the axis of the device. Such a device is extremely compact, lightweight and characterized by reduced power requirements. There is additionally provided an improved radio frequency coupling member, which cooperates with the magnetic focusing means. The coupling member, to effect the desired purpose, may be provided with a longitudinal slot.

Accordingly, it is an object of the present invention to provide an improved slow wave propagating electron discharge device.

Another object of the present invention is to provide a compact and lightweight high-power slow wave propagating device.

Another object of the present invention is to provide in an electron discharge device means for utilizing the slow wave propagating structure for providing a magnetic focusing field.

A still further object is to provide in connection with a pulsed high power slow wave propagating electron discharge device having a suitable electron beam trajectory, means for eliminating the necessity of any external electron beam field control means.

A further object is to provide in a slow Wave propagating device periodic electron beam focusing field means.

A further object lies in the provision of an improved Fig. 1;

with the accompanying drawings, wherein the'invention is embodied in concrete form, and in which I Fig. 1 is a longitudinal view, mainly in cross section, of a preferred form of the present invention;

Fig. 2 is a diagrammatical representation, useful in explaining the operation of, for instance, the device of Fig.1;

Fig. 3 is an enlarged cross-sectional view of a portion of the structure of the device of Fig. l; I I

Fig. 4 is a block diagram of a modulator, which may be used in conjunction with, for example, the device of Fig. 5 is a circuit diagram of the magnetizing pulse generator of a part of the modulator of Fig. 4;

Fig. 6 is a graphic representation, useful for explaining the principles of operation of the circuit of FigfS;

Fig. 7 is a longitudinal view, mainly in cross. section of a modification of the device of 'Fig. l; I

Fig. 8 is a fragmentary'view, showing a further modification of the device of Fig. 1;'

Fig. 9 is a longitudinal view, mainly in cross section, of an alternate embodiment of the present invention;

Fig. 10 is a longitudinal view, mainly in cross section, of a further embodiment of the present invention; and

Fig. 11 is a cross-sectioned view of the device of Fig. 10 taken along lines 1111 thereof.

Similar characters of reference are used in all of th above figures to indicate corresponding parts.

In Fig. 1 there is provided means, including for example electron emitter or cathode button 16, for producing an electron beam, with the cathode button 16 aligned along the longitudinal axis 17 of the electron discharge device. Positioned to receive the electron beam in energyexchanging relation is a. means defining a slow wave propagating structure, such as cylindrical helix 18. Adjacent one end of the helix 18 is aradio frequency input means, such as rectangular wave guide 19, which has an impedance-matching plunger 21 arranged at one end thereof. For providing translatory 'movement ,of the plunger 21 along the axis of the wave guide 19, activating member 22 may be rigidly secured to the plunger'2l; At the radio frequency entrance end of the helix 18 there is disposed a radio frequency coupling member, such as tube 23, which is electrically connected for transmission of radio frequency or microwave energy to the helix 18. At the output end of the helix 18 there is provided a means for abstracting radio frequency energy from the helix 18, which means may include output wave guide 27.

Throughout the major portion of the helix 18, the pitch may be uniform; however, at the electromagnetic energy input and output regions of the helix 18, which are electrically coupled for radio frequency energy to the tubes 23, 30, the pitch may be greater, becoming progressively smaller to match the uniform pitch of the helix 18 approximately in the region between the points 24, 25, which uniform pitch portion may be designated 35.

If desired, a coil 26 may be employed in the vicinity of the tube 23, which upon energizat-ion is effective for providing a trimmer magnetic field for focusing the electron beam, as will be explained more fully hereinbelow.

The previously-referred-to cathode button 16 is provided with its active surface suitably oxide coated and substantially spherically concave in cross section about the longitudinal axis 17. The edge of the aperture of the apertured cup 28, which is supported by sleeve 29, provides a first line conductor or edge 31 positioned outwardly of and along the longitudinal axis 17 in a direction away from the cathode'button 16 Accordingly, it willbe noted that the diameter of the aperture of cup "28 is larger than the diameter of the cathode button 16.

The end of the sleeve 29 in a direction .toward the main body of flue electron discharge device provides a second lineconductor or edge 32, with the second edge 32 being locatedoutwardly of the cathodebutton '16 ton greater extent than the first-edge 31. The second edge 32 is, in addition, disposed along the longitudinal axis: 17 .in a direction away "from the .cathodebutton 16 to a greater extent than the first edge 31, The first and second line conductors ior edges .31, .32 constitute an electrostaticfield forming aneans or 'focusing'lectrode33, which is similar to that disclosed and claimed in applicants co-pending application .S.v .N. 81,480, entitled Charged Particle .Beam Forming Apparatus,-- filed .MarchlfS, .1949, now U. S. Patent.2,564,743, dated August .21, 1195.1. 7

For accelerating and :directing :electrons emanating 'from the outward button 16 toward the main body of the electron discharge device, an accelerating electrode or anode 34 is provided, which anode 34 is suitably energized byan external potential source, as discussed .hereinbelow. The cathode button 16, focusing electrode33 and 'the anode 34comprise an elcctron'gun forforming a high density electron .beam in whichwtheindividual electrons thereof traverse substantially rectilinear trajectories and travel toward a point. i

To preserve -..the internal vacuum of the device the cylindrical helix 1 8 is coaxially-disposed within a vitreous envelope 36 which is joined at one end to anode 34 by means .of annular member 37 and apertured disc-38, with all or the connections being efiected in-a vacuum tight manner. At the other end of the helix 18 a similar vacuum-tight connection of the envelope 36 is efiected to the cylindrical-member39-by means of annular member 41. If-desired, a coil 26 may be employed in the yicinity -of the coupling tube 30.

v For, the collection of electrons an electron collector '42 is positioned to receive electrons after their exchange of energy with the helix 18. The collector 42 is formed of .an apertured tubular member 43, which is joined to coaxially -disposed tubes 44, 46. Between the tubes 44, 46is a iluid-conductingpipe 47, by means of which heat developed incollector 42 may be removed from the dis? charge device. The cylindrical member '39, which partially surrounds the collector 42 is joined to a further cylindrical member 48in a vaccum tight manner by means of a vitreous tubular seal 49. Closing the end 'of the further cylindrical member 48 is a disc 51, with the -=connection therebetween effected in a manner suitable to preserve the internal vacuum 'of-the' discharge device. lo the same end, the fluid conducting pipe 47 is similarly joinedto the .disc v51.

:In the. device of Fig. 1 there is additionally provided means for confining electrons to desired trajectories,

a pulsed character and may be substantially established 'in -synchronism with the pulsed electron beam. In Fig. 2

there .isshown a diagrammatic representation of a pulsed electron beam, as represented by curve 52. The pulse of'magnetizing current, which is introduced into the helix 18, may .be represented by curve '53, withcurve 53 having asuhstantially flat portion or constant-amplitude portion rduring the time tha't the pulse 52is operative. Moreover, the :arrangement'provides for the establishment of the magnetic ifocn'sing field of *sufiicient magnitude prior 4 to the injection of electrons into the helix 18, as represented by curve 52.

As shown more clearly in Fig. 3, the helix 18 extends through the tubes 23, 30. For convenience, the part of the helix 18 extending from the opposed ends 54, 56 of the tubes 23 and 30 maybe designated helix portion 57. By reason of this arrangement, a suitable magnetic focusing field may be maintained in the region, for instance, between the anode 34 and the end 54 of coupling tube 23, with the helix portion 58 contained within the tube 23 being insulated therefrom by means of tubular insulator 59. To prevent the tube 23 from acting as a short-circuited secondary of a "transformer, a longitudinal slot 60 is provided therein. Helix'portion 57,.which is electrically coupled to]: microwave frequency energy to the end 54 of tube 23, is effective for radio frequency interaction with an electron beam. By maintaining the pitch of the helix portion 58 similar to that of the pitch of the helix portion 35, that is, that part between the points 24, 25, these regions of the helix 18 are suitable for providing :a magnetic focusing field of substantially. the same strength. V

To this end, the cross-sectional configuration of the helix portion 58 may be rectangular so that its internal diameter .is substantially the :same as that of the helix portion 135. Moreover, the cross-sectional area of the helix portions 35, 58 may be substantially the same, thereby insuring substantially equal current carrying capacities for the portions 35, 58. By reason of this arrangement helix portions 57, 58 may be effective for providing magnetic focusing fields of substantially the same strength.

In .order to provide an input connection for focusing current to helix portion '58, which is electrically continuous with helix portion 57, the end of helix portion 58 may be formed in a lead 61, which may be for electrical conduction secured, as by soldering, to the annular member 37. It will be understood that a further helix portion, similar to helix portion 57, may be contained within coupling tube 30.

Viewed somewhat differently, it may be said that a slow Wave propagating structure or helix is provided by helix portion 57 and that additional helices are provided substantially surrounded by coupling tubes 23, 30, which may be connected to and integral with the'aforemen tioned helix, for the passage of a magnetic-focusing current.

In Fig. 4 a pulse generator or modulatoris illustrated, Which is suitable for energizing the device of Fig. l. A control pulse emanating from synchronizer 62 is eflective for controlling a magnetizing pulse generator 63 having output leads 64, 66 which may be connectedto annular members 37, 41 respectively of the device of Fig. .1. The control pulse emanating from the synchronizer 6.2 is .further coupled to the power supply 67 by way of a delay circuit 68, with the powersupply 67 having output leads 69, 71, whichmaybeconnected to the cathode button .16 .and the anode 34 respectively. It will be understood that these connections, if desired, :may be made through suitable input leads at the base of the discharge device of .Fig. l. The output pulsesemanati-ng rom the magnetizing pulse generator 63 and the power supply 67 .mayhave the same Waveform'and relative-time relation as the curves 53, 52, respectively, of Fig. 2.

.If desired the synchronizer pulse emanating from the delay circuit 68 may be employed to control a radio fre-- quency driver 72 having an ouput coupling means '73, which may be electrically coupled to wave guide 19.

in operation, electrons emanating from the cathode button 16, under the influence of the focusing electrode 33 and the anode 34 are formed into an electron beam, in which the individual electrons thereof traverse subs't antially rectilinear trajectories and travel toward a'po'int located in thejvicinity of the aperture ofthe anode 34. Thus, it will be noted that the electron beam is form'ed substantially through electrostatic focusing means with the magnetic field substantially excluded from the cathode region, including for instance the cathode button 16.

To insure that substantially none of the magnetic lines of force thread the cathode region, anode 34 may be formed of magnetic material and formed with a skirt 7%. However, in view of the pulsed nature of the magnetic focusing field, if desired, anode 34 may be formed of a highly conductive material, such as copper. Such an arrangement insures the exclusion of the magnetic field from the cathode region by reason of eddy currents flowing in such a copper member under the influence of a pulsed magnetic field.

Radio frequency energy, may be coupled to the helix portion 57 by introduction through wave guide 19. Upon leaving the tube 23 the electron beam traverses the length thereof in energy exchanging relationship. More specifically, the electron beam initially abstracts energy from the electromagnetic energy passing through the turns of the helix portion 57. Subsequent thereto the electron beam, which has become density modulated in the process, is effective for delivering radio frequency energy to the helix portion 57. Such electromagnetic energy may be abstracted from the helix portion 57 at its output end by means of wave guide 27.

Simultaneously with the radio frequency energy interchange between the electron beam and the helix portion 57, a magnetic focusing field, which is established by introducing direct current into the helix 18, is effective for focusing the electron beam throughout its traverse of the helix portion 57. Furthermore, with additional helices, such as helix portion 58, included within the tubes 23, 30, the magnetic focusing field extends along the entire length of the helix 18. As a result, a magnetic focusing field is established by current passing through helix 18, which field is effective for confining electrons to desired trajectories substantially from the time they leave the anode 34 until they enter the collector 42.

Thus, the electron beam throughout its transit of the entire helix 18 is subjected to a magnetic focusing field emanating from the helix 18. By reason of the uniform pitch of the helix portions 58 and uniform pitch helix portion 57 the magnetic field established thereby has a substantially axially symmetrical configuration. In the region of the helix 18 between the ends 54, 56 of the tubes 23, 30 and points 24, 25 where the pitch is variable, the helix 18 may not be effective for providing a symmetrical axially-directed magnetic field. To compensate for this nonuniformity, an additional magnetic flux, provided by coils 26, 26' may be useful.

If desired, the pitch of the helix 18 may be made uniform throughout its length, including those helix portions adjacent coupling tubes 23, 30. This arrangement has the advantage of obtaining a symmetrical axiallydirected magnetic field emanating from the helix 18 for the control of the trajectories of the electrons of the beam. It will be noted that the opposed ends of the coupling tubes 23 and 30 extend linearly and are formed at approximately 45 angles with respect to the axis 17. With the proposed uniform pitch for the helix 18 the aforementioned ends of the tubes 23 may be formed with curved shapes or other complex configurations.

If desired, coils 26, 26' may be replaced by coils of a few turns connected in series with the helix 18.

In Fig. 5 means are provided for pulsing a load having a relatively large reactive component. Before discussing the circuit of Fig. 5 it is useful to consider other types of pulsing circuits, including the hard tube modulator and the artificial line modulator. The hard tube modulator is characterized by high vacuum electron discharge devices, which inherently are limited as to current carrying capacity. To avoid such difficulty, the artificial line modulator has been provided, which is characterized by its high current handling capacity and customarily includes gaseous electron discharge devices, such as thyratrons. In the design of such a line modulator, an attempt is made to operate with a pure resistance load, in order to avoid excessive dissipation of power. More particularly, there is an attempt to match the characteristic impedance of the artificial or delay line-to the impedance of the load. It is apparent that with a load constituted of a large inductance, it is necessary to introduce a large series resistance therewith to preserve the waveform. In such case, the losses involved in the circuit would become prohibitive, thereby relegating against tie use of a line modulator.

It also appears that where energy storage circuits, including for instance a delay line or a condenser, have been employed, the power which is released from such storage circuits is dissipated. According to the present invention, means are provided for circulating energy from one storage circuit to another in a substantially lossless manner. By this arrangement, there is considerable saving in the drive power required in view of the fact that only a small amount of power is dissipated in the switching device and other small circuit resistances.

In Fig. 5 a pulse forming circuit is provided, which includes energy storage means, such as condenser 74, connected in a first loop I through a current controlling means, such as thyratron 76, to terminals 77, 78. Connected in series with terminals 77, 73, is a further energy storage circuit, which may be constituted by a means defining a slow wave propagating structure, and represented in Fig. 5 by its electrical equivalents, that is inductor 79 having an internal resistance 81. By periodically releasing energy from the condenser 74 by activation of the current control grid 82 of the thyratron 76, the inductor 79 may be periodically pulsed so as to set up an axially-directed magnetic field, which field may be useful for controlling the trajectories of electrons.

Condenser 74 is also connected in loop II to an additional energy storage circuit, such as inductor 83 having an internal resistance 84. Also included in loop II is a variable source of potential, such as battery 86 and means for controlling the direction of current flow, such as holding or blocking diode 87. On the assumption of an initial condition of a positive charge being present on the upper plate 88 of condenser 74 and the activation of current flow in loop I by means of the firing of thyratron 76, the polarity of the condenser 74 will reverse so that the lower plate 89 of the condenser 74 will become positively charged. Loop II is effective in restoring the original charge of the condenser 74, that is, a positive charge associated with the upper plate 88. The circuit of Fig. 5 achieves the circulation of energy back and forth through the inductor 79 Without involving any sizeable dissipation of power. The only drive power required for the operation of the circuit of Fig. 5 is that arising from losses in the thyratron 76, diode 87 and other small circuit resistances, such as resistances 81, 84.

In a steady operation of a simple inductance-capacitance circuit, the maximum voltage across the condenser is maintained in quadrature relationship with respect to the maximum current. By permitting the capacitor of such a circuit to reverse the polarity of its voltage from a positive maximum to a negative minimum, the current increases from zero to a maximum and decreases to zero again. In other words, while the capacitor voltage undergoes the aforementioned variation, the current experiences a half-cycle pulse.

More particularly, in Fig. 5, it may be assumed that the upper plate 88 of the condenser 74 is at a positive potential at the start of a cycle having a period T. By activating the control grid 82 of the thyratron 76, the condenser 74 may be permitted to discharge through the inductor 79 and resistance 81. Under these circumstances, as shown more clearly in the graphical representation of Fig. 6, the voltage of the condenser 74, as represented by curve 91, reverses its polarity, so

, in loop 1.

"7 that the lower plate '89 thereof at the end of current flow in the loop II, as represented by curve 92, has a positive polarity.

Inconnection with the .thyratron 76 it may be pointed out that assuming the voltage thereacross is suitable for the conduction of current, the grid 82 is effective for controlling the thing or conduction of current therethrough provided that the thyratron 76 is deionized. Further mention will be made of the importance of the deionization of the thyratron 76 subsequent to the discussion of the operation of loop II o the circuit of Fig. 5.

The inductor 83 receives current therethrough as shown more clearly in Fig. 6, with the battery 86 suitable for providing the aforementioned small dissipation of power associated with the circuit resistance. T s, during the time that current is passing in loop ii, the polarity of the condenser 74 is restored to its initial condition. The holding diode 37 included in loop II is effective during the passage of current in loop I for preventing the flow of current through loop ll.

By defining the pulse period and the duty cycle T and a, respectively, T indicates the. time during which 79 of loop I sothat the chargingperiod 5T is of suffn ciently long duration to maintain the voltage of the condenser 74 negative during the time that the thyratron 76 deionizes. The current flow through loop 11 has a half sine waveform similar to the current waveform of loop I, with the exception that it is longer in duration and smaller in amplitude.

The voltage across the thyratron 76 immediately prior to conduction of current theret'nrough is of a magnitude equal to the voltage across the condenser Upon the "firing of'the thyr'atron '76, the voltage thereacross drops to a small magnitude and remains substantially constant throughout the time that current is conducted More particularly, the voltage across the thyratron 76 will have during the time off a smallamplitude, which could be represented by a horizontal line spaced a small distance above the zero'axis of Fig. 6. At the end of current conduction in loop I, the voltage across the thyratron 76 decreases to that of the voltage across 'the condenser 74 and follows the voltage of the condenser 74 during the remainder of the time T, that is, until the start of the next pulse cycle. the voltage across the inductor 79 and resistance 81 may be determined by taking the difi'erence of the voltages across the condenser 74 and thyratron 76.

The geographical representations of Fig. 6 indicate slightly idealized conditions, which however, appear to be amply justified by the operation of the circuit of Fig. 5. Owing to the fact that during the latter half of the time ctT or during conduction of current in loop I, the polarity of the condenser 74 is such as to tend to cause cuncntaflow in loop II. More particularly, the lower plate 89 of the condenser 74 assumes a positive potential, which is favorable for the flow of current through loop H. However, the magnitude of such current flow is negligible and may be disregarded in the present analysis.

As previously indicated, the thyratron 7 5 may pass current if it is not in a deionized condition. During the time'fiT, from Fig. 6 it will be noted that the voltage of the condenser 74, as represented by curve 91, changes 'in a timeless than that required for the thyratron 76 to deioni'ze, current would again start flowing in loop I.

It is apparent that I "8 By selecting essentially the magnitudes :of. the inductors 79, 83, this difficulty may be :avoided. With the time during the ,BT portion of the cycle during which the condenser 74 changes its polarity from a negative maximum to substantially zero voltage at a value greater than the deionization time of the 'thyratron 76, spurious current flow in loop I may be substantially eliminated.

If desired, a current step-up transformer may "be associated withloop I of the circuit :of Fig. .5. 'In such case, a coil 94 may be inductively coupled to inductor with inductor 79 and .coil 94 forming the primary and secondary of the transformer 96, respectively. The coil 94 is provided with terminals 97, $8 which 'may be connected to annular members 37, 41, respectively, that is, to the helix :18 of the device of Fig. 1; Thus, this arrangement is particularly useful where it is desired to employ a relatively large .magnitude of magnetic focusing current in the helix 18, thereby permitting a sub stantially smaller magnitude of current to be conducted in loop I of the circuit of Fig. .5. 1

If desired, in the circuit of Fig. 5 the condenser 74 and the thyrat'ron 76 may be interchanged. This arrangemerit permits the cathode of thyratron 76 to be maintained at ground potential. It will be noted that in this proposed modification energy is circulated from one energy storage-circuit to another; without involving any substantial dissipation of power.

*If. desired, the thyratron 76 in the circuit of .Fig. 5 may be replaced byaa high vacuum electron discharge device. This 'modification'makes possible the formation of pulses having a length unrelated to the deionization time of gaseous-electrondischarge devices, such a'sthyratron 76. As previously discussed, the time :for the grid 82 of "the tliyratron 76 to :regain control thereof is 'an important consideration. However, by reason of the currently proposed modification a'ny -'difficulties associated therewith may be avoided. It will, of course, be understood that a step-up transformer, such as transformer "96, may be useful for providing the desired magnitude of current.

As thus .far described, the circuit of Fig. 5 has been shown to be eilective for producing pulses of current; It will be understood that it is also useful for the production of voltage pulses. For example, a negative voltage pulse appears across the condenser 74, as'sho'wn by curve 91 of Fig' 6. Such a voltage pulse may be useful in connection with an accelerating electrode or anode for the production of an electron beam.

By way of example, in the device of Fig. 1 a'c'apacitance is present between the cathode button 16 and the anode 34, which may correspond to the condenser 74 of the circuit of Fig. 5. --In this arrangement, the holding diode -87 may be replaced by a gaseous discharge device, such as a thyratron, the firing of which may be useful for controlling the nlow of current in loop I I. Accordingly, this arrangement permits the formation of a flat-topped voltage pulse. In addition, if desired the thyratron 76 maybe replaced by a high vacuum electron discharge device, in the event thatit is desired to produce a pulse havingfia length substantially less than the deionization time of a gas tube, 'suchas thyratron 76.

The circuit of Fig. 5 may be further modified for the production of voltage pulses, by replacing the condenser 74 with a :coil forming the primary of a transformer. The secondary of this transformer may then be coupled to the capacitance formed by 'a cathode and its accelerating electrode, such as cathode but-ton 16 and anode 34 of the device'of Pig. 1. For operation at a high voltageand low current, the thyratron 76 may be replaced by a high vacuum elect-ron'discharge device.

If desired, an additional accelerating electrode may be employed in the device of Fig. 1. Such additional electrode may be insulated from and maintained at a substantially lower potential than anode 34. Under such circumstances, such additional accelerating elec-trode may be pulsed at a substantially lower voltage, such as a tenth of the voltage maintained between the cathode button 16 and the anode 34. This arrangement permits the pulsing of the electron beam at a lower voltage level, and is somewhat analogous to the action occurring in a triode tube, wherein the grid is effective for controlling the passage of current.

While the possible modifications of the current of Fig. relating to the production of voltage pulses are useful in connection with slow wave propagating structures, such as the device of Fig. 1, it will be understood that such modifications are equally applicable to other types of electron discharge devices, such as klystrons. By way of illustration in this connection reference may be had to a velocity modulation electron discharge device, suitable for utilizing the proposed circuit modifications. More particularly, the capacitance of the condenser 74 could be replaced by the capacitance between the cathode button and the anode of the discharge devices shown in application S. N. 117,187, entitled High Frequency Beam Tube Device, in the name of Charles E. Rich et al., filed September 22, 1949, and assigned to the same assignee as the present application, now U. S. Patent 2,687,490, dated August 24, 1954. If desired, an additional accelerating electrode could be employed or the accelerating electrode shown therein could be insulated from the main body of the tube and maintained at a lower potential.

In Fig. 7 there is shown a modification of the device of Fig. 1 in which the coil 26 is replaced by an electromagnet 90 having aperture 95 to accommodate input and output wave guides 19, 27, respectively. The electromagnet 90 may be constituted of magnetic frame 99 energized by coil 100. If desired, by omitting coil 100, the structure may take the form of a permanent magnet.

As previously discussed, owing to the non-uniformity of pitch in portions of the helix 18 the magnetic field established by the introduction of current therein may not be completely axially symmetrical. Thus, in the region of, for instance, the end 54 of coupling tube 23 the magnetic field emanating from the helix 18 may have components which are directed out of the paper of the drawing. The electromagnet 90 is effective for providing additional focusing in such regions.

' *In addition, by varying the position of the electromagnet 90 or other magnetic structure, such as coil 26 of the device of Fig. 1, the lack of uniformity in the magnetic field established by the helix :18 in the region of the end 54 of the coupling tube 23 may be compensated for, thereby maintaining a substantially axiallydirected magnetic field throughout the length of the helix 18. Under such circumstances, the control of the trajectories of the electrons of the beam may be more readily achieved.

In Fig. 8 a further modification of the device of Fig. 1 is shown, in which a transition section is employed, which is generally similar to that shown in application S. N. 97,070, entitled High Frequency Coupling Device, in the name of Calvin F. Quate, filed June 3, 1949, and assigned to Leland Stanford University, now abandoned. The transition section 101 is formed of a tubular conductor 102, which is provided with a slot 103, the pitch of which changes continuously and smoothly throughout the length of the conductor 102. At the end of the transition section 101 remote from the anode 34 the conductor 102 joins a helix 104, which has a uniform pitch and generally corresponds to helix portion 57 of the device of Fig. 1. At the end of the conductor 102 facing the anode 34, the slot 103 is substantially parallel to the axis 17, that is, the pitch has an infinite value;

The width of the slot 103 may be made approximately the same as the space between adjacent turns of the helix 104. The pitch of the slot 103 decreases toward the end of the conductor 102, where it joins the helix 104. At

the point where the conductor 102 and helix 104 join, the pitch of the slot 103 may be substantially the same as that of the helix 104, and the width of the conductor between adjacent convolutions of the slot 103 may be substantially equal to the width or the diameter of the conductor forming the helix 104.

To couple magnetization current to the conductor 102, which is electrically connected to the helix 104, lead 105 is provided, which is joined to annular member 37. The transition section 101 is effective for coupling electromagnetic energy to the helix 104. Surrounding a portion of the conductor 102 is a metallic band 106 which is electrically connected to the inner conductor 107 of an input coaxial line 108, which has its outer conductor 109 joined to tubular member 111.

In operation, electromagnetic energy is coupled to the device by way of coaxial transmission line 108. Within tubular member 111 in the vicinity of the band 106, electromagnetic energy exists in the principal or TEM mode, with the velocity of wave propagation substantially the same as in free space. More particularly, the electric field is radially directed and the magnetic field lines are disposed in concentric circles around the conductor 102.

In the required mode of operation in the helix 104, the electric field lines curve from one turn to another, both inside and outside the helix 104. The resultant electric field inside the helix 104 extends substantially axially, being directed oppositely at half-Wavelength intervals. Since the velocity of axial propagation is relatively low, these intervals are considerably shorter than half-wavelengths in free space. The transition section 101 is effective for accomplishing the desired result.

By introducing magnetic focusing current through lead 105 into the conductor 102, which in turn is electrically coupled to helix portion 104, a magnetic focusing field may be established substantially in synchronism with an electron beam, in the same manner as that previously described in connection with the device of Fig. 1. The modulator of Fig. 4 may be employed, if desired.

In Fig. 9 there is shown a further modification of the device of Fig. 1, wherein a magnetic focusing field is provided by an external solenoid 112. In this arrangement, the helix 113 extending from the opposed ends 114, 116 of the radio frequency coupling tubes 117, is generally similar to that portion of the helix 18 extending between the ends 54, 56 of the coupling tubes 23, 30 or, stated difierently, helix portion 57 of Fig. 1. In Fig. 9 the coupling tubes 117 are formed without a longitudinal slot and are substantially hollow, that is, they are formed without a helix portion 58 (Fig. 3). Thus, in Fig. 9 the helix 113 is effective solely in connection with the interchange of radio frequency energy with the electron beam and is not instrumental in establishing a magnetic focusing field.

For the energization of the device of Fig. 9 the circuit of Fig. 4 may be employed, with leads 64, 66 thereof coupled to leads 118, 119 of coil 112. In addition, leads 69, 71 may extend to the cathode (now shown) and the anode 34 of the device of Fig. 9. By reason of this arrangement the focusing field, provided by coil 112, may be established substantially in synchronism with a pulsed electron beam.

Except for the changes introduced by reason of the structural differences the operation of the device of Fig. 9 is essentially similar to that of the device of Fig. 1.

By means of the pulse operation of the device of Fig. 9, which includes the pulsed control of the solenoid 112 in synchronism with the electron beam, a compact lightweight electron discharge device characterized by small power consumption is provided. An appreciation of these and related properties of the device may be gained by considering the weight and heat dissipation properties of the components, such as for example solenoid 112.

At the outset, it may be noted that the heat dissipation can be reduced by increasing the weight of components, such as solenoid 112. Several factors may be taken '11 into consideration, including the weight of the compo;- nents, such as solenoid-112, the weight and the capacity of the power supply such as parts of the circnit of Fig. 5, means for cooling, and so forth.

The solenoid 112 may have a length I, an internal diameter 2x, an average diameter d, and a thickness c.

The cylindrical helix may have a diameter 2b.. The ratio of the thickness 6 to the average diameter d of the solenoid 112 may be defined as q. Thus, the average diameter d of the solenoid 112 may be stated to be i V 2a;

2 Y h V q The ratio of the total area occupied by the conductor to that of the gross area in connection with the solenoid 112 is the space factor 5. Further with regard to the solenoid 112 the gross volume may be designated U, the heat loss P, the resistivity p, and the total ampere turns NI. It

follows that The inductance L and resistance R of a solenoid 112 where l/c 1, l/d l, that is, for a long coil, is

L= [0.O250.0162q] 10- (11 N' 1rd &r R scl ql p 12) Accordingly,

gwhzs-doiea (13) R 1r p In Equations 11, 12 and 13 unit length is in inches, R in ohms, L in henries, and current in amperes.

The significance of Equations 2 to 13 may be explained as follows, a is the average diameter of the solenoid 112, q is the geometrical factor which is the ratio of the thickness of the solenoid 112 to the mean diameter d of the solenoid 112, and x is the inner radius of the solenoid 112. In order for the solenoid 112 to be maintained free from electrical interaction with the radio frequency field of the helix 113, x must be large compared to b, the radius of the helix 113. When x and q are selected, the volume occupied by the solenoid lizmay be determined by Equation 3. After it is decided how many ampere turns per unit length are to be provided by the solenoid 1 12, and the resistivity p of the material and the space factor s of the solenoid 112 is known, Equation '4 may be used to determine the power consumption or PR loss of the solenoid 11-2 per unit length. Equations 3 and 4 give the Generally speaking, the value of q mustbe selected in 7 terms of the power density which may be associatedwith the particular material. By way of illnstrat'ionga coil, such as solenoid 112, formed of fdrmaxcopper wire with free air circulation may be employed on the basi's'o'f 600 circular mils for every ampere the who carries. On the other hand, if the wire is formed of copper tubing with cooling water circulation, the allowable power and cur rent density can be-materially higher. Therefore, the highest permissible ower density sets a lower limit for q. The power density Pd, as set forth in Equati'On S, ntayee used as a design parameter. This together with the given constants, Nl/l, p, 2):, s, may be grouped together has {me normalization constant 1 as defined-in Equatieh 7; 7

When the power density Pd is fixed, as setfor'th in F Equation 8 ,11 is defined. When the magnitudes o'f' 'the and power consumptionof the solenoid 112 maybe redefined in terms 'of 1;, as in Equations"9 and 10.

As previously discussed, the device of Fig. 9 may be energized by the modulator of Fig; 4, including the cireuitof Fig. "5. It is deemed useful to discussth'e inductor 83 together with its resistance 84, with the inductarree and resistance thereof, -for convenience, designated L2 and R2, respectively. In general, we ma employ subscripts 1' and 2 in connection with the solenoid 112 and inductor 83, respectively.

We may first consider the weight and heat dissipation of the inductor 83 'ineluded in loop '11 of the' 'circiiit'of Fig. 5. It can be shown that the maximum energy storage in inductor 83 must be the same as the peak energ storage in inductor 79 included in loop I. In der to minimize power dissipation in the-combinationrbf inductor 83 and resistance 84, it is desirable to employ a eoil having a high ratio of inductance to resistance. For convenience, such a coil may be de'sigriated inductor 83, 'it'being'understood fhatthe resistance 84 is assoeia'ted therewith. The inductor 83 may have an average radiiis y, and a thickness and length equal sub'staiftially to y. The inductance L2 and R2 of such an indiic'tor 83 may be stated, as follows: 7

where p'a 'is the resistivity, s2 "is the space faster, and Us is the volume of the inductor83.

The ratio of Lz/Rz is 13 From Equation 19 it appears that the power dissipation in the inductor 83 may be greatly reduced below that of the peak power dissipation of the solenoid 112, if the radius yz is selected as' large in comparison with radius x, and if the duty cycle of loop I of the circuit of Fig. 5 is made low. In this connection it will be recalled that the terminals 77, 78 of Fig. 5 may be connected to the opposite ends of the helix 18 of the device of Fig. 1. The foregoing analysis is equally applicable to such an arrangement with the quantities suitably adjusted. This may be conveniently, for example, accomplished by considering the helix 18 of Fig. 1 as the solenoid 112 of Fig. 9, that is, the inner diameter of the helix 18 may be taken as 2x, the average diameter of the helix 18 as d, the diameter of the helix 18 as c, and the length of the helix 18 as I. It may be pointed out that where the helix 18 is arranged to produce the magnetic field, the spacing factor may be shown to be In Figs. and 11 there is shown an electron discharge device of the slow wave propagating variety, which is similar to the device of Fig. 1 in that the slow wave propagating structure is useful for establishing both a radio frequency field and a magnetic focusing field. Means are provided defining a slow wave propagating structure, such as cylindrical helices 125, 130, the opposed ends of which are substantially abutting. By reason of the arrangement both helices 125, 130 are effective in connection with the interchange of radio frequency energy with an electron beam.

A cathode button 121, energizable by means of leads 122, 123, is effective-in conjunction with an accelerating electrode or' anode 124, for producing an electron beam with the anode 124 maintained at a suitable potential by means of lead 126. The electron beam after its traverse of helix 130 may be collected by electron collector 127. Radio frequency energy may be introduced into and abstracted from the electron discharge device by means of input fiat spiral 128 and output flat spiral 129, respectively.

'At the opposed ends of the helices 125, 130, means are provided for interrupting the slow wave propagating structure, such as helices 125, 130, which means may include an apertured disc 131. The disc 131 may be formed of an insulating material, such as 'fused quartz, and a dissipative coating may be provided by painting the disc 131 with a carbon suspension, such as the substance commonly known as Aquadag. The coating is preferably distributed over both sides of the disc 131 in approximately sectoral areas 120, as shown more clearly in Fig. 11, with a generally star-shaped portion 135 of the disc 131 uncoated. Surrounding the disc 131 are additional flat spirals 132, 133, which are connected to leads 134, 136, respectively. The inner ends of flat spirals 132, 133, as well as inner ends of flat spirals 128, 129 may be coupled to or made continuous with the helices 118, 119. The outer ends of spirals 128, 129 may be connected to leads 137, 138 through inner conductors 139, 141, respectively. I

To establish a magnetic focusing field, magnetic focusing current may be introduced into the helices 125, 130 by use of current pulser 142 and transformer 144.

In operation, electrons emanating from the cathode button 121 under the influence of the accelerating electrode 124 are formed into an electron beam, which traverses in succession the helices 125, 130. Radio frequency energy. coupled to the input end of helix 125 by means of flat spiral 128 is amplified by reason of the interaction of by means of flat spiral 129.

By employing plural sections foi a cylindrical helix, such as helix 118 of the device of Fig. 1, different magnitudes of magnetic focusing current may be employed in connection with the aforementioned plural sections. Such plural sections may be constituted of helices 125, 130 as illustrated in the device of Fig. 10. If desired, the arrangement permits the accurate control of the trajectory of an electron beam in terms of the equilibrium radius, that is, the distance at which the space charge repulsion forces balance the magnetic field forces. A discussion of this type of electron beam control is presented in applicants co-pending application S. N. 186,730, entitled High Frequency Apparatus, filed September 26, 1950, noW'U. S. Patent 2,741,718, dated April 10, 1956. In addition, if desired, the device of Fig. l, or any of its modifications may be operated according to such principles.

In the device of Fig. 10, the magnetic focusing current introduced into the helix by means of leads 134, 137 may be of a different magnitude than that introduced into helix by means of leads 136, 138. In this manner, it is possible to achieve an improved control of the electron beam trajectory. By way of illustration it will be recalled that the electron beam in traversing the helices 125, 130 undergoes density modulation so that, owing to the increased space charge repulsion forces, it may be desirable to employ a magnetic focusing field of greater intensity in connection with helix 130.

Where it is contemplated to employ a pulsed electron beam, the magnetic field may be established in synchronism with such a beam by means of the current pulser 142. In this connection, the modulator of Fig. 4, together with the magnetizing pulse generator of Fig. 5 may be useful. More particularly, leads 69, 71 of the power supply 67 may be connected to leads 122, 126 of the device of Fig. 10. In addition, the current transformer 144 of the device of Fig. 10 may be generally similar to the current transformer 96 of the circuit of Fig. 5.

Thus, the electron discharge device provides a means for separately energizing various portions of a slow Wave propagating structure, which structure is useful for establishing a magnetic focusing field. Other details of the discharge device of Figs. 10 and 11 are discussed in co-pending application S. N. 171,479, entitled Travelling Wave Tubes, filed June 30, 1950, in the name of Lester M. Field, and assigned to Leland Stanford University, now U. S. Patent 2,712,614, dated July 5, 1955.

While the device of Fig. 10 is particularly useful in connection with the pulsed operation of a slow wave propagating electron discharge device, it will be understood that, if desired, continuous wave operation may be employed. In this connection, the device provides for the establishing of the magnetic focusing field by means of helices 125, 130 in such a manner that different magnitudes of magnetic focusing fields may be employed in conjunction with different portions of an electron beam.

The device of Fig. 10, may include, if desired, the synchronous pulsing of the radio frequency energy introduced therein, by means of flat spiral 128, together with the electron beam and magnetic focusing field. In addition, if desired the cathode structure, including the cathode button 16, focusing electrode 33 and the anode 34, of, for example, Fig. 1, may be employed in substitution in part or in whole for the cathode button 121 and anode 124. Moreover, if desired external magnetic focusing coils, such as solenoid 112 of Fig. 9 may be employed to produce magnetic fields of different strength along the axis of the electron beam, thereby providing for a more accurate control of the trajectories of the electrons thereof.

It is apparent that many changes could be made in the construction of the device discussed hereinabove and that many apparently different embodiments of the invention could be made Without departing from the scope thereof. For example, many of the structural arrangements, while particularly suitable for pulsed operation, are also suitable for continuous wave operation. Accordingly, it is high frequency source means.

intended that all matter contained in the above description or's io'w'n in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is. V

'1. An ultra high frequency apparatus comprising'means for producing an electron stream directed along a 'prede t'erfnined axis, a slow wave propagating structure assoelated with the stream producing means and extending along said axis, a source of radio frequencyenergy, radio frequency input means coupling energy from said source to the slow wave propagating structure for transmitting ultra high frequency energy along the slow wave propagatingstructure in the direction of travel of the electron stream, electromagnetic focusing means extending along said axis, and pulse generating means electrically connected to the electromagnetic focusing means for supplying pulsed excitation current to the electromagnetic focusing means, said pulse generating means being coupled to the electron stream producing means and said source for synchronously pulsing the energy output of the electron stream producing means and ultra high frequency. source with the pulsing of the electromagnetic focusing means. I 7

2. An ultra high frequency apparatus as defined in claim 1 wherein the slow wave propagating structure and electromagnetic focusing means include a common helical conductor. a

=3. An ultra high frequency apparatus as defined in claim 1 wherein the pulse generating means include means 7 for exciting said focusing means a longer pulse time duration than the stream producing means and the ultra 4. -An ultra high frequency apparatus comprising means for producing an electron stream directed along a predetermined axis, a slow wave propagating structure associated with the stream producing means and extending along said axis, electromagnetic focusing means extending along said axis, and means coupled to said electron stream producing means and said focusing means for synchronously pulsing the electron stream producing .means and the electromagnetic focusing means.

5. High frequency travelling wave tube apparatus, comprising electron gun means for producing and directing -an electron beam having a boundary of predetermined configuration along a linear axis, a collector longitudinally spaced along said axis from said gun for receiving said electron beam, highly conductive helix means comprising a slow wave propagating structure for high frequency electromagnetic waves extending along said axis between said collector and said electron gun means and positioned for interaction of electromagnetic waves propagated along said helix means with said beam, envelope-defining means about said axis for maintaining said beam and said helix means in a vacuum, conductor means electrically connected to opposite ends of said set forth in claim 5, wherein said conductor means com-.

prises first and second tubular conductors in coaxial relatio'nship with said helix means at opposite ends thereof, said tubular conductors having substantially the same diameter as said helix means with the helix end of each tubular conductor terminating on a bias angle with respect 7 to said predetermined axis, longitudinal slot means in each of said tubular conductors, and first and second hollow wave guides each having a pair of apertures through opposite wave guide walls for receiving said helix means and tubular conductors with the helix end energized.

.16 portions of said first and second tubular conductor-s being in the interiors of said first and's'econd wave guides, respec'tiv'ely, for coupling of electromagnetic energy be tween said wave guides and said helix means.

7. Ultra high frequency apparatus comprising means for producing an electron stream directed'along a .pre determined axis, a tubular conductive member having a variable pitch helical slot, a helix of conductive material connected to one end of the tubular member, the helix and tubular member being axially aligned with the electron stream producingmeans along said'predetermined axis for passage of the'el'ectron stream successively 7 through the tubular conductor and helix, means electrical producing an electron stream directed along a predetermined axis, two coaxially-dispo'sed cylindrical helices aligned along said axis and having their opposed ends substantially abutting, energizing means connected across said helices for introducing dilfe'rent magnitudes of current into each of said helices, whereby said helices Eprovide magnetic focusing fields of different strength, and means for synchronously pulsing the electron stream producing means and said energizing means.

' 9. High frequency travelling Wave tube-apparatus, coinprising a vacuum envelope having ali'near axis, a highly conductive helix having a region of substantiallyconstant diameter extending along the axis of said envelope, said helix comprising means for propagating slow wave electromagnetic energy, electron gun means ationeend of 7 said helix for producing and directing an electron beam for travel along said axis within said envelope for interaction with electromagnetic energy propagated along said helix, collector means at the other end of said helix 'for receiving said beam,'means including a source of pulsed unidirectional voltage coupled to said helix 'for producing a magnetizing current pulses for passage by said helix along a helical path for providing an axial magnetic beam controlling field for' maintaining the diameter of said electron beamsubstantiallyconstant along saidhelix, and means coupled to beam producing "means for pulsing said beam in synchronisfnwith said magnetizing current pulses.

1'0. High frequency apparatus comprising an elongated vacuum tube having a longitudinal axis, coil means extending along said axis, means for generating a stream of electrons directed along the axis of the tube and through said coil means, the coil means when energized producing a magnetic field extending substantially parallel to the electron stream in the region of the stream, pulse generating means electrically connected to the coil means for passing pulsed unidirectional current through the coil means, and means operatively associated with the electron stream generating means for interrupting the electron stream, the stream interrupting means being'synchronized with the pulse generating means whereby the str'eam of electrons flows only during the time the coil means is 11. High frequency apparatus comprising an elongated vacuum tube having a longitudinal axis, a helix of conductive material extending along the axis of the tube, means for generating a stream of electrons directed along the axis of the tube and through said helix, pulse generating means electrically connected to the helix for passing pulsed unidirectionalcurrent through the helix, the helix when energized producing a magnetic field extending substantially parallel to the electron streai'nin the "region of the stream, means for coupling ultra high frequency energy to the helix for p'rdpa'gation 'tlierealong in the direction of the electron stream, and means operatively 17 associated with the electron stream generating means for interrupting the electron stream, the stream interrupting means being synchronized with the pulse generating means whereby the stream of electrons flows only during the time the helix is pulsed with unidirectional current.

12. High frequency travelling Wave tube apparatus as set forth in claim 5, further including means coupled to said electron gun means for pulsing said electron beam, means coupled to said supply terminals external of said envelope defining means for supplying a pulsating unidirectional current to said helix means for providing a pulsed magnetic focusing field, and means coupled to said last two-named means for substantially synchronizing the pulsing of the electron beam and the magnetic focusing field.

References Cited in the file of this patent UNITED STATES PATENTS 2,439,401 Smith Apr. 13, 1948 2,516,944 Barnett Aug. 1, 1950 2,541,843 Tiley Feb. 13, l951 2,546,848 Wideroe Mar. 27, 1951 2,672,572 Tiley Mar. 16, 1954 

